Retracted noise suppression system

ABSTRACT

A mechanism for attenuating sound pressure levels in the fluid passageways of an aircraft jet engine comprising a plurality of pivotally attached vane members each having a pair of oppositely facing acoustically treated surfaces. The vane members are stowed for cruise flight in positions aligned along and parallel to the wall of the passageway, wherein fluid flow occurs over only one of said oppositely facing surfaces. The vanes are pivotable along axes parallel to the flow into operative noise suppression positions perpendicular to said wall in which flow occurs over each of said surfaces, thereby increasing attenuation of sound pressure levels in said passageway. The preferred embodiment involves a turbofan jet engine wherein the vane members are stowed along an outer wall in overlapping fashion and the means for pivotally moving the members comprises a power actuated ring member which pivotally displaces each vane into a radial position wherein adjacent vanes cooperate to form trapezoidal acoustic chambers to reflect and dampen sound pressure wave fronts.

United States Patent [72] Inventors Edwin W. Bond Issaquah; Robert L.Lundeen, Seattle, both of Wash. [21] Appl. No. 46,049 [22] Filed June15, 1970 [45] Patented Nov.9,l97l [73] Assignee The Boeing CompanySeattle, Wash.

[54] RETRACTED NOISE SUPPRESSION SYSTEM 4 Claims, 9 Drawing Figs.

52 115.131 181/3311D, 181/33 G, 181/50, 181/64, 239/265.13, 239/265.3951 1111. c1 ..B64d 33/06,

FOln 1/08 [50] FieldofSearch ..F01n/1/18;18l/33,331-1A, 33 HB, 33 BC, 33HD, 33 G, 43, 51, 42, 50, 64; 239/1273, 265.11, 265.13, 265.17, 265.33,265.37, 265.39, 265.41 [56] References Cited UNITED STATES PATENTS3,113,634 12/1963 Watters... 181/33 3,477,231 11/1969 Paulson... 181/33G 3,533,486 10/1970 Paulson 181/50 FOREIGN PATENTS 1,525,355 4/1968France .1 181/33 HD 921,127 3/1963 Great Britain 181/33 HA PrimaryExaminer-Robert S. Ward, Jr, Attorneys-Glenn Orlob and Bernard A.Donahue ABSTRACT: A mechanism for attenuating sound pressure levels inthe fluid passageways of an aircraft jet engine comprising a pluralityof pivotally attached vane members each having a pair of oppositelyfacing acoustically treated surfaces. The vane members are stowed forcruise flight in positions aligned along and parallel to the wall of thepassageway, wherein fluid flow occurs over only one of said oppositelyfacing surfaces. The vanesare pivotable along axes parallel to the flowinto operative noise suppression positions perpendicular to said wall inwhich flow occurs over each of said surfaces, thereby increasingattenuation of sound pressure levels in said passageway. The preferredembodiment involves a turbofan jet engine wherein the vane members arestowed along an outer wall in overlapping fashion and the means forpivotally moving the members comprises a power actuated ring memberwhich pivotally displaces each vane into a radial posi tion whereinadjacent vanes cooperate to form trapezoidal acoustic chambers toreflect and dampen sound pressure wave fronts.

PATENTEUunv 9 IEWI 3, 18,700

' sum 1 or 2 INVENTORB, EDW/N M BOND BY ROBERT L. LU/YDEEN Law/d ATTOAWE V I Pmmanunv elem 3.618.700

' sum 2 OF 2 INVENTORS, EDM/V w so/vp L BY Poe/5W L. Ll/NDEEN ATTORNEYRETRACTED NOISE SUPPRESSION SYSTEM FIELD OF THE INVENTION DESCRIPTION OFTHE PRIOR ART It has been a recent practice to line all availablewettedsurfaces within an inlet or exhaust passageway with acousticallytreated sound absorbingmaterials in order to maximize attenuation ofsound emitted from the passageway. It is known that the addition of moretreated surfaces byplacing fixed members carrying acoustical surfacesinthefluidstream will further reduce sound levels. However, thisexpedient has not been widely used as it seriously interferes with theaerodynamic efficiency of the passageway during cruise flight, whenmaximum efficiency is required for economical operation.

It has also been'known in certain complex prior artnoise suppressionsystems to deploy fingerlike members in an exhaustpassageway for thepurpose of breaking up or redirecting flow patterns into smallerindividual streams or passageways. However, such fingerlike members arerelatively small and are used only for redirecting flow patterns orchanging sound frequencies rather than attenuating sound pressurelevels. Deployable fingerlike or plate members havealso been used tochoke air inlet passageways, thereby increasing fluid velocities tonear-sonic magnitude to minimize theescape of noise upstream out of theforward end of the engine.

SUMMARY OF THE INVENTION It is the general object of this invention toprovide a simple mechanism for selectively obtaining increased noiseattenuation during low-speed flight which does not adversely affectcruiseperformance.

It is aprimary object of this invention to :provide means for increasingthe wetted area of acoustically treatedsurface in an engine passagewayduring low-speed flight which can be returned to a stowed positionduring cruise for minimum interference with aerodynamic efficiency ofthe passageway.

A related object of this invention is to provide a retractable vanemember noise suppression system in which the vanes are arranged suchthat more vanes, and hence more wetted surface area in the operativeposition, may be conveniently designed into'the system merely by spacingthe vanes closer together and allowing them to overlap in the stowedposition.

A further related objective of this invention is to provide anacoustically treated vane system of the class described in which thevanes, when deployed, are so arranged that each adjacent pair of vanemembers will cooperate with the walls of an annular passageway toestablish sound suppression chambers which will serve to reflect anddampen moving sound pressure level wave fronts. The above objectives areeach achieved in the disclosed preferred embodiment of this invention,which was engineered for a particular turbofan engine and set of noiseregulations, by the provision of some 28 acoustically treated vanemembers pivotally attached along the outer wall of the fan exhaust alongaxes which are parallel to the direction of flow in the passageway. Thevane members are stowed for cruise flight in overlapping fashion alongand parallel to the wall, thereby preventing flow over one of theacoustic surfaces of each member. A power-actuated ring member isoperably connected to each vane member, and upon actuation willpivotally rotate each vane into an operative position where each vaneextends radially substantially across the annular turbofan passageway,and where the entirely of both the acoustic surfaces of each vane isexposed to fluid flow, thereby more than doubling the exposed area ofacoustic surface material, and increasing the attenuation of soundpressure levels accordingly. Each adjacent pair of vanes cooperates toestablish a trapezoidal chamber for sound attenuation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation section view ofan aircraft turbofan jet engineand nacelle-structure wherein the fanexhaust duct is equipped with applicants retractable 'sound suppressionsystem, shown in the stowed position for cruise flight.

FIG. 2 is an elevation section view similar to FIG. lshowing applicantssystem in the operative position for maximum sound suppression duringlow-speed flight.

FIG. 3 is a rear section view taken along lines 3-3 in FIG. 1

FIG. 4 is a plan view showing applicants noise attenuating vane membersstowed for cruise flight taken at 4-4 in FIG. 3.

FIG. 5 is a section view through a vane member taken at 5- 5 in FIG. 4.

FIG. 6 is a rear section view similar to FIG. 3 taken' along lines 6-6in FIG. 2 showing the vane members in an operative position.

FIG.'7 is a detailed plan view of applicants vane member,

'hingefitting, and power actuated ring member taken at 7-7 FIG. 8 is asection view through the hinge fitting and vane member taken at 8-8 inFIG. 7 showing the vane deployed in an operative position.

FIG. 8A is a section view similar to FIG. 8 showing the vane members inthe stowed position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. '1, ahighbypass ratio turbofan engine 10 is shown to include a forward fancowling 12, an intake centerbody 14, a fan casing 16, and'an aft fancowling 18. Enginecenterbody 20 can be seen to form an interior wall ofan annular exhaust passageway 22; the exterior wall of this passagewaybeing formed by the aft fan cowling 18. As will imity with, the localcurvature of the engine centerbody 20. As

will be made clearer by subsequent figures, a power-actuated ring member34 is operably connected to each vane member 30, and, upon actuation,will rotate each vane into or out of either the operative position ofFIG. 2 or the stowed position of FIG. 1.

FIG. 3 is a fragmented rear section view taken at 3-3 in FIG. 1, showingthe vane members 30 held in stowed positions for cruise flight. The vanemembers 30 are held in overlapping stowed positions such that flow ofexhaust fluid occurs over only a portion of the inner one of the pair ofoppositely facing exterior surfaces of each vane member 30. As will be 7discussed more fully in connection with FIG. 5, each of the oppositelyfacing exterior surfaces is acoustically treated to maximize soundattenuation. Therefore, in the stowed position of FIG. 3, the vanemember has substantially more than half of its acoustically treatedsurface area shielded from the fluid flow within the passageway. Also,it should be noted that in the stowed position the total exposed vanemember surface area is substantially the same as the surface area of acircular outer wall of a conventional turbofan exhaust passageway. Thepower actuated ring member 34 can be seen to be connected to each vanemember 30 at each vane lug 36 by means of links 38, and to be holdingthe members against the passageway fairing 40.

FIG. 4, taken at 4-4 in FIG. 3, is a plan view showing the overlappingof the leaflike vane members 30. In the stowed position shown, eachmember 30 has its outermost exterior surface resting against either thepassageway fairing 40 or the innermost surface of the next adjacentmember 30. The plan form of each of the members 30 is tailored for themaximum area which will fit into the passageway 22 when the members aredeployed into the radially extending operative positions of FIG. 2. Thetaper at the forward edge of each member is arranged for clearance withthrust reverser blocker flaps of a generally conventional type (notshown). The aft end of each member is tapered to clear the noule exitplane and ancillary equipment such as a variable area plug nozzle. Eachperipheral edge other than the hinged edge is tapered and faired foraerodynamic cleanliness in either the stowed or operative position, asis best shown in the FIG. 5 edge section view taken at 5-5 in FIG. 4.

The FIG. 5 section view depicts the vane member 30 as comprising acentral web 42, an inner honeycomb core 44, an outer honeycomb core 46,an outer perforated sheet exterior skin 48, an inner perforated sheetexterior skin 50, and a relatively sharp tip juncture 51. As will beunderstood by persons skilled in the acoustics art, the perforatedsheets are provided with apertures of selected size, spacing andarrangement relative to the depth and size of the adjacent honeycombcore cells for maximum attenuation of sound pressure levels in selectedfrequency ranges. The web member, honeycomb core and skins areintegrally constructed, e.g., by bonding, and connected to a hingefitting to form a rigid vane member.

FIG. 6 is a view similar to the FIG. 3 rear view, showing the vanemembers 30 radially deployed in operative positions extendingsubstantially across the annular passageway 22. The power actuated ring34 has been circumferentially displaced clockwise (as shown) from thestowed position of FIG. 3, thereby rotating each vane member clockwiseabout pivot pin 52 by means of the link 38 and lug 36. Each adjacentpair of vane members 30 can be seen to form a generally trapezoidalchamber 53 bounded at the inner end by the centerbody and at the outerend by the passageway fairing 40. Each trapezoidal chamber thus formedserves to trap and dampen reflecting sound pressure wave fronts inmotion with the chamber. The surfaces of centerbody 20 and fairing 40are preferably each acoustically treated for maximum attenuation.

FIG. 7 is a detailed plan view, taken at 7-7 in FIG. 6, ofa structuralpivot fitting 60 and the hinge portion 32 of a vane member 30. The pivotpin 52 is affixed to hinge portion 32 for movement therewith. Thefitting 60 is preferably a machined casting which includes fitting lugs62, 64, and 66, within which the pivot pin 52 is free to rotate. Thehinge portion 32 is likewise preferably a machined casting whichincludes a pair of lugs 36 disposed and arranged for attachment to ring34 through side links 38 by means of pivot pins as shown. In thisembodiment the hinge portion 32 further includes means for centering thering member 34 with respect to the lugs 36, in the form of a centeringguide lug 70, having a contoured surface 72, serving to preventundesired lateral motion of the ring, and to support the ring concentricwith the engine passageway.

A detailed section of the hinge-to-ring attachment is provided by FIG.8, taken at 8-8 in FIG. 7. The hinge fitting 60 is rigidly affixed tothe aft cowl l8, and pivotally supports pivot pin 52 and hinge portion32. The power-actuated ring 34 is nested against contoured surface 72 ofguide lug 70, and connected to the vane lug 36 by pin-ended links 38.The vane member 30 is depicted in an operative position radiallydeployed in the annular passageway.

FIG. 8A is a detailed section similar to FIG. 8 with the exception thatthe vane members 30 are shown held in their stowed positions. The poweractuated ring 34 has been displaced counterclockwise as shown, therebyrotating the vane members 30 into their stowed positions, in which eachouter surface skin 48 is in nesting contact with its correspondingsupport surface 40. The particular embodiment shown involves specificgeometric and acoustic restraints wherein the vane members have beensized to extend across the passageway and also are spaced apart adistance less than their radial len th, and therefore they necessariloverlap when stowed. T e support surfaces 40 are prefera ly located suchthat in the overlap areas the inner surface skins 50 are in nestingcontact with the outer surface skins 48 of the next adjacent vanemember, thereby preventing undesired stray flow patterns betweenmembers.

Based on the foregoing description, it is apparent that applicantssystem provides a relatively simple means for selectively increasing thewetted area of acoustic materials in an engine fluid passageway where itis desired to maximize sound attenuation, and further that thisobjective is achieved with a minimum of interference with propulsiveefficiency when the system is returned to the stowed position for highspeed cruise flight. Many variations of the preferred embodiment shownwill be apparent to persons skilled in this art. For example, it willreadily be recognized that increasing the spacing between vane members30 could eliminate overlapping of the vane members in the stowedposition. If this reduction in sound absorption capability isacceptable, a cleaner aerodynamic passageway wall and a simplerinstallation will result. It is also apparent that the apparatusconcepts involved here are applicable to either an engine inletpassageway or a primary exhaust passageway with no more than routineengineering modifications. Therefore, it is intended in the appendedclaims to cover all such variations and modifications.

What we claim and desired to be secured by Letters Patent is:

1. In combination with a jet engine having annular exhaust passagewaywalls formed by an outer cowling structure and the engine center bodystructure, a mechanism for attenuating sound pressure levels comprising:

a plurality of vane members having oppositely facing exterior surfaceswhich are acoustically treated; said vane members being pivotallymounted within said passageway on said outer cowling structure on axesaligned parallel to the direction of flow of exhaust gases, and being sosized and spaced apart from one another that they may be radiallydeployed to extend substantially across said annular passageway tothereby form a substantially closed trapezoidal chamber between eachadjacent vane member to reflect and dampen sound pressure levels withinsaid passageway; and means for pivotally moving said vane members fromtheir radially deployed positions into stowed positions adjacent to thesurface of the outer cowling surface and wherein the outer face of eachvane member is disposed in overlapping fashion upon the inner face of anext adjacent vane member to thereby prevent stray airflow between vanemembers and to minimize drag within the passageway for cruise flight.

2. The mechanism of claim 1 wherein said means for pivotally moving saidvane members comprises a power actuated ring member which is operablyconnected to each of said vane members.

3. The mechanism of claim 1 wherein said vane members comprise thinaerodynamically clean airfoil sections having tapered leading andtrailing edges which extend substantially across said annular passagewaywhen disposed in said operative positions.

4. The mechanism of claim 3 wherein each of said vane members comprises:

perforated sheet exterior skin members,

honeycomb core attached to said skin members,

a hinge fitting connected to said honeycomb core having a lug memberdisposed for attachment to said means for pivotally moving said members,

wherein said skin members, honeycomb core and hinge fittings areintegrally constructed and connected to form a rigid vane member, andwherein said hinge fitting further comprises means for centering saidring member with respect to said vane member.

1. In combination with a jet engine having annular exhaust passagewaywalls formed by an outer cowling structure and the engine center bodystructure, a mechanism for attenuating sound pressure levels comprising:a plurality of vane members having oppositely facing exterior surfaceswhich are acoustically treated; said vane members being pivotallymounted within said passageway on said outer cowling structure on axesaligned parallel to the direction of flow of exhaust gases, and being sosized and spaced apart from one another that they may Be radiallydeployed to extend substantially across said annular passageway tothereby form a substantially closed trapezoidal chamber between eachadjacent vane member to reflect and dampen sound pressure levels withinsaid passageway; and means for pivotally moving said vane members fromtheir radially deployed positions into stowed positions adjacent to thesurface of the outer cowling surface and wherein the outer face of eachvane member is disposed in overlapping fashion upon the inner face of anext adjacent vane member to thereby prevent stray airflow between vanemembers and to minimize drag within the passageway for cruise flight. 2.The mechanism of claim 1 wherein said means for pivotally moving saidvane members comprises a power actuated ring member which is operablyconnected to each of said vane members.
 3. The mechanism of claim 1wherein said vane members comprise thin aerodynamically clean airfoilsections having tapered leading and trailing edges which extendsubstantially across said annular passageway when disposed in saidoperative positions.
 4. The mechanism of claim 3 wherein each of saidvane members comprises: perforated sheet exterior skin members,honeycomb core attached to said skin members, a hinge fitting connectedto said honeycomb core having a lug member disposed for attachment tosaid means for pivotally moving said members, wherein said skin members,honeycomb core and hinge fittings are integrally constructed andconnected to form a rigid vane member, and wherein said hinge fittingfurther comprises means for centering said ring member with respect tosaid vane member.